Relight impossible with zero fuel flow!
Note - read with caution: 1st post from a non airman.
First QRH check item in an ENG RESTART IN FLIGHT is:
FUEL SUPPLY .............. CHECK.
(OK, admittedly my source used is the ATR 72-500's QRH)
According to the investigators (see post #239), at time 53:19 the crew discussed that engine #1 was feathered and noted that it's fuel supply was cutoff. That's because they had manually flicked the fuel cutoff CL on the O/H panel as per standard shutdown sequence, right?
Investigators said the crew then "decided to attempt restart of #1."
Problem was, they left the fuel cutoff CL in the OFF position for the next 56 seconds (from 53:23 until 54:19 on the FDR trace), during which the investigators noted several attempts at relight were tried unsuccessfully.
Others here have noted evidence of a successful relight of engine #1 during the A/C's last airborne 15 seconds or so, that is, AFTER the fuel supply was manually turned back ON.
If only ...